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Oldsmobile L47 specs: 244 ci (4.0L) 8-cylinder, 3.425 x 3.307 in (87 x 84 mm) bore and stroke, 10.3:1 compression. Rated 250 hp. Rod ratio and piston speed.
The Oldsmobile Aurora (L47) is close to square: 3.4252" bore against 3.3071" stroke, within 3.6%, which splits the difference between a high-revving layout and a torque layout. The 3.3071" stroke does not reach 4,000 ft/min of mean piston speed until about 7,250 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 30.5 ci (500 cc).
10.3:1 on aluminum heads is in the range that usually runs on pump premium; aluminum sheds heat faster than iron, which makes the same number a little more forgiving.
Factory fitments include the Aurora, Oldsmobile Aurora.
| Displacement | 244 ci / 4 L |
|---|---|
| Bore | 3.4252" |
| Stroke | 3.3071" |
| Cylinders | 8 |
| Compression ratio | 10.3:1 |
| Bore/stroke ratio | 1.036 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 250 hp |
| Bore/stroke character | 1.036 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,307 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.5 ci |
| Static compression | 10.3:1 — in the range that usually runs on pump premium |
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